Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $223.96   13.202%   $253.5272   $253.53   $253.55   $253.50  
  Purchase #2 $105.37   11.361%   $117.3411   $117.34   $117.35   $117.30  
  Purchase #3 $201.49   10.524%   $222.6948   $222.69   $222.70   $222.70  
  Purchase #4 $239.76   3.309%   $247.6937   $247.69   $247.70   $247.70  
  Purchase #5 $183.68   11.652%   $205.0824   $205.08   $205.10   $205.10  
  Purchase #6 $242.61   6.752%   $258.991   $258.99   $259.00   $259.00  
  Purchase #7 $102.89   9.821%   $112.9948   $112.99   $113.00   $113.00  
  7 purchase totals = $1,299.76       $1,418.3250   $1,418.31   $1,418.40   $1,418.30